Currently there is a trend in telecommunication systems based on self-organising overlay networks e.g. using peer to peer technologies to reduce investments in centralised infrastructure nodes. Such overlay networks are used for distributed data storage, e.g. for user and location information, registrar functions etc. They provide optimized routing based on a “neighbourhood relationship”.
Such a telecommunication system could for instance comprise entities ranging from a mobile presence server, a multi media phone to nearly any kind of device e.g. in a next generation network like the new IP Multimedia Subsystem (IMS).
Therefore it is necessary to provide the usual basic functionalities for such type of overlay networks. A well known and widely used services in traditional telecommunication networks is presence awareness.
In traditional networks usually a central presence server is used where a subscriber's presence state is maintained. The server notifies all subscribers that are interested in the published presence information, if the respective subscribers have admissible privileges. A major problem in traditional presence processing is that the client of a subscriber can suddenly disappear, without telling the server that it is going offline.
Aliveness tests such as “ping” mechanisms are used to regularly confirm that the subscriber's client is still present, i.e. reachable and alive. If in a centralized approach this node has to serve a huge number of users, this is correlated with a challenging high concentration of load and communication.
Such a server is disclosed in the U.S. Pat. No. 6,463,471. There one can find a peer-to-peer presence system using a central server for downloading the presence information about subscribers. It is clearly stated, that nodes i.e. subscriber's clients have to be regularly “pinged” in order to detect an off-line state.
The patent discloses a method for distributing and maintaining network presence information. According to an embodiment of the present invention, a user logs onto the Internet and transmits to a presence (information) server presence information, a list of peers (individual network users) whose network presence are of interest to the user, and a request for a list of peers interested in the user's network presence. The presence server then responds to the user with both a list including the last known Internet Protocol (IP) address for each peer the user is interested in and a list of peers interested in the user's Internet presence. The user then attempts to directly contact the peers on the first list by confirming and authenticating the received IP addresses. According to a policy, the user directly contacts the peers on the second list to inform those peers the user is currently signed on-line. Finally, the user periodically “pings” (directly contacts) the confirmed and authenticated IP addresses from the first list received from the IPIS to determine when those peers sign off-line. The drawback of these approaches is, that it either causes a huge load on a centralized server, or relay on frequent messages between peers to detect the offline state within a certain time frame.
The remaining problem is to provide a presence system that enables effective presence management with fast detection of leaving users without centralised server and minimized network and terminal load.